Extended Data Fig. 5. Ion chromatograms of unmodified rS1 and in vitro RNAylated rS1 extracted from LC-MS/MS data.

Extracted ion chromatograms (XICs) for triply and quadruply charged precursor ions (monoisotopic masses 1115.8096 and 837.1090, respectively). XICs were extracted using Skyline⁵⁹, an open source document editor for creating and analysing targeted proteomics experiments. The masses correspond to an rS1 peptide AFLPGSLVDVRPVRDTLHLEGK with an attached ADPr-cytidine. Recombinant S1 domain 2 was in vitro incubated with ModB and one of the following components: a, no other supplements, b, uncapped RNA-8mer, c, NAD-RNA-8mer, d, NAD-RNA-8mer treated with RNase A and T1 (results in ADPr-cytidine adducts). An elution peak at 42.3 min is observable in d and corresponds to the peptide modified with ADPr-cytosine. Spurious intensities can be observed in c and might represent a degradation product. a and b show only background/contaminant peaks. A contaminant peak at 40 min can be also observed in d (consider the difference in the intensity scale between d and a-c).